Homicide is a show based on David Simon's book about spending a year inside the Homicide department of Baltimore. You know David Simon from co-creating The Wire. The show was based on his book with most of the characters altered b/c the book was straight up journalism on real people.
They put together one of the best ensemble casts ever made, had top tier guest casting and, as it was a Baltimore production, you'll see tons of the Bmore & East Coast actor faces you know from The Wire & The Sopranos in here. In an era where TV acting was seen as a lower tier, Barry Levinson's name on it helped get great character actors from film like Yaphet Kotto, Ned Beatty & Jon Pulito alongside people regarded as some of the best since like Andre Braugher and Melissa Leo. Also, the character who's appeared in the most television shows in history started right here as Richard Belzer's Detective Munch debuts in the first episode.
It was also one of the best written shows out and still stands up despite being on network TV in the 90s. And the music was great and set the template for most the music montages in shows since.
David Simon himself didn't get involved in the show early on besides submitting a script w/ David Mills in SSN 2 (with a heavy performance by Robin Williams and a baby Jake Gyllenhaal) but eventually joined in SSN 4 where Tom Fontana helped to teach him all the ins and outs of a television show and led to his eventual making of The Corner and The Wire after Homicide ended.
Now, being a network show, Fontana had his issues with the network's interference and airing episodes out of order, so, he took his frustrations and made the most un-network show ever at HBO: OZ. Their first scripted drama comes directly from the people of Homicide including shooting in Baltimore with many of the same crew.
The after Oz' success came Sopranos, Deadwood, The Corner, The Wire, etc... and then FX follows with The Shield (The Wire & The Shield both have their pilots and series finales directed by Clark Johnson, one of the leads of Homicide for all 7 seasons & the movie), then AMC and others follow suit, but you don't get any of it without Homicide.
It's the cornerstone of prestige TV.
just in case 
